The present invention relates generally to the field of waveguides. In particular, the present invention relates to compositions suitable for use in forming flexible optical waveguides. The invention further relates to methods of forming flexible optical waveguides. As well, the invention relates to flexible optical waveguides and to electronic devices that include a flexible optical waveguide.
Signal transmission using pulse sequences of light is becoming increasingly important in high-speed communications. For example, optical integrated circuits (OICs) are gaining importance for high bandwidth optical interconnects. As a result, the integration of optical components such as waveguides, filters, optical interconnects, lenses, diffraction gratings, and the like, is becoming increasingly important.
Optical waveguides are typically constructed by surrounding a core material with a clad layer. Optical radiation propagates in the core material because the clad layer has a lower index of refraction than the core material. Waveguides may be used individually or as an array supported on a substrate. The waveguides often perform a passive function on the optical radiation. For example, splitters divide an optical signal in one waveguide into two or more waveguides; couplers add an optical signal from two or more waveguides into a smaller number of waveguides; and wavelength division multiplexing (“WDM”) structures separate an input optical signal into spectrally discrete output signals, each of which couples to separate waveguides, usually by employing either phase array designs or gratings. Spectral filters, polarizers, and isolators may be incorporated into the waveguide. As well, waveguides may alternatively contain active functionality, wherein the input signal is altered by interaction with a second optical or electrical signal. Exemplary active functionality includes amplification and switching such as with electro-optic, thermo-optic or acousto-optic devices.
Waveguide substrates include, for example silicon wafers and circuit backplanes for use in server devices. The ability to handle waveguides without crack defects in the core and/or cladding materials is desirable. The cracking property generally is a result of brittleness in the coating material. Many organic polymer-based waveguides such as polyimides are flexible, but have other drawbacks such as moisture absorption, high losses and expense. Silicon-based systems, which address various shortcomings of organic polymer systems, are generally brittle resulting in crack defects as a result of handling.
Photoimageable waveguide cores have been proposed wherein portions of the coating are dissolved in an organic solvent to generate the desired structures. This technique has the drawback of using organic solvents that are difficult to dispose of, waste treat and/or contain in a closed environment. It is therefore desirable to have the option of using aqueous developers to create waveguide structures from photoimageable coatings.
Hybrid silicon-carbon polymer systems have been proposed which address brittleness in interlayer dielectric coatings, especially for pore generating compositions, for microcircuit applications. (See, e.g., Chandross et al, U.S. Pat. No. 6,251,486) disclose a modified methylsilsesquioxane composition for use as a low dielectric material. The methylsilsesquioxane includes dimethyl and phenyl pendant groups to provide better crack resistance than an all methylsilsesquioxane. Thus, crack resistance is achieved for the coated article through incorporation of the pendant groups into the polymer prior to coating. The choice of pendant groups and amounts are limited. It would, therefore, be desirable to improve flexibility by use of a component separate from the polymer in the composition being coated, as this would allow for an increase in the choices and amounts of suitable materials. There is thus a need in the art for compositions suitable for use in manufacturing optical waveguides, which compositions provide beneficial flexibility characteristics while also being developable in an aqueous developer solution. As well, there is a need in the art for waveguides formed from these compositions, for methods of forming such waveguides, and for electronic devices that include such waveguides.